The invention relates to yarns and multi-fibers comprised of metallized stainless steel monofilaments suitable for use as RFI/EMI shielding materials and other purposes.
As the complexity of electronic systems in aerospace applications has grown, designers of the cables that interconnect system components have been obliged to meet increasingly stringent requirements for RFI/EMI protection and, because aircraft performance and operating cost are directly related to weight, demand for lighter weight cable constructions. In conventional designs, cables are protected against RFI/EMI by wire mesh shields that are braided over the insulation that surrounds the cable core. In more demanding applications, additional shielding protection can be achieved with the use of a separately braided or knitted wire mesh sleeve that fits over one or more cables. Conventional shielding materials consist of single strand, tin-, nickel, or silver-plated copper wire, typically #34 or #36 AWG (6.3 or 5.0 mils diameter respectively).
Although functionally suitable in the past, these materials cannot satisfy the more stringent shielding and weight requirements imposed on new cable designs. Leakage occurs in shields fabricated from conventional plated copper wires due to gaps in the mesh where the wires intersect. In addition, the stiffness of the metal wire used in braiding prevents the mesh from tightly conforming to the surface of the core insulation, leaving small gaps that have the effect of limiting the frequency range over which the cable can be operationally effective. Braided wire mesh fabricated from smaller diameter wires would presumably improve shielding effectiveness as well as reduce cable weight but copper wires finer than #36 AWG are too prone to breakage in the braiding process.